Actuators are used for example in fuel injection systems. Such actuators have a variable-length region having piezoelements which expand or are compressed depending on an applied voltage. In multilayer actuators or piezo-multilayer actuators such as are used in the fuel injection systems, having a layered arrangement of the piezoelements, for example the operating temperature is one aspect which affects the lifetime of this component. In some applications, nevertheless, the temperature is not monitored.
In order to detect an operating range that limits the lifetime or possible incipient damage of the component, it is desirable to monitor the temperature of the component, for example by means of a sensor system.
Temperature sensors thermally coupled to the actuator can be used for temperature monitoring. These separate, non-integrated sensors require additional structural space. Moreover, they are not suitable for detecting the core temperature of the component. Depending on thermal resistances of the materials used and the specific design, the measured temperature can differ significantly from the core temperature of the actuator.
A further possibility for temperature detection comprises determining temperature information from the value of the small-signal capacitance of the actuator. However, this method has only a limited accuracy. Moreover, the measured value is corrupted by the pyroelectric characteristic of the piezoceramic (PZT) material used. Moreover, the linear small-signal measurement required for this type of temperature detection is complicated to combine with the large-signal driving of the actuator, thus giving rise to additional costs for the electronics.